By Quentin Fottrell

E-books brought erotica out of the bedroom and onto public transportation. But with the wild success of the bondage-themed “Fifty Shades of Grey” novels, experts say readers may now be in for a deluge of dirty words.

“Fifty Shades of Grey,” which might not even have been published prior to the Amazon Kindle, sold 10 million copies since March. Available initially just in e-book form, the books are helping to bring what was a niche genre to general audiences, publishers say. Back in April, the digital version of the book  was reportedly selling six times faster than the print one, although now it is a bestseller in both forms. One-in-three romantic and erotic books sold last year were e-books, according to the Romance Writers of America.  That’s compared to one in five for books overall, according to the American Association of Publishers. “Our racier content has always sold more in our e-book retail channels than other titles,” says Brian Matthews, a spokesman for e-publisher Lulu. E-books seem to be not only driving sales of erotic works, they are helping them go mainstream, he says.

By stripping romance and erotic novels books of their steamy covers, e-readers eliminated much of the embarrassment of toting them around, experts say. With e-books, no one can tell if you’re reading Faulkner of Fabio, says Alina Adams, an e-book consultant.”That’s allowed a lot more people to buy them without worry.” And e-readers made it possible for people to read erotic or pornographic novels while they’re sitting in the doctor’s office, the playground or on the subway, says Mark Coker, founder of Smashwords.com, a distributor of self-published e-books.

But selling them in digital format also allows publishers to cheaply test the appetite for certain books heavy on sex — and sometimes light on literary merit — without having to splurge on marketing and distribution costs for paperbacks, Matthews says. In fact, some publishing houses have even opened departments specializing in erotic e-books. Harper Collins recently launched Michief, an erotic e-book publishing arm, and signed 60 new authors. The company declined to comment. (Harper Collins is part of News Corp., which also owns SmartMoney.com.) Plus, not all bookstores or libraries will stock erotic fiction, Matthews says. Fifty Shades of Grey was pulled from some libraries in Wisconsin and Florida.

Despite such pushback, publishers say they’re rushing to release racy content as e-books, according to publishers of exotic fiction. Kensington Books – which includes titles like Canyon Shadows and Unexpected Pleasures –says its Aphrodisia collection of erotic e-books accounted for nearly 60% of sales in 2011, compared to only 2% in 2008. “Fifty Shades of Grey” has put erotica in mainstream media, mainstream stores and the public eye, says Vida Engstrand, a spokeswoman for Kensington Books. Tina Haveman, founder and CEO of Xtasy Books says there’s been an increase in sales of erotic romance since “Fifty Shades of Grey” was released in the U.S. and a five-fold increase in sales since the Kindle was released over two years ago. “People even read the smaller novellas on their phones,” Haveman says.

E-rotic e-books are just one more instance of sex driving technological innovation, experts say. Patchen Barss, author of The Erotic Engine, says sexuality fueled technological and artistic developments  including cave drawings, VHS tapes, and photo-sharing sites like Flickr and YouTube. People often get a new thrill from viewing the same old erotic material in a new format, he says:  “It’s exciting to transfer a pornographic film from Super 8 to digital.” And e-books continue a long tradition of people concealing erotica on their person. For instance, Victorian gentleman used to carry pornographic Stanhope microphotographs in their pocket watches. “The same is true for carrying e-books today,” he says. “It’s like wearing kinky underwear.”